Carburetor



A. C. BENNETT Aug. 19, 1958 CARBURETOR Filed Sept. 21, 1954 M/UN Wm m

m y A NW N? a W m a fi O (IARBURETOR Arthur C. Bennett, Penfield, N. Y.,assignor to General Motors Corporation, Detroit, Mich., a corporation ofDelaware Application September 21, E54, Serial No. 457,436

ll Claim. (Cl. 26l39) This invention relates to carburetors for internalcombustion engines, particularly engines for automotive vehicles andmore specifically to automatic choke mechanism operable to automaticallycontrol the position of an air inlet valve for the purpose ofcontrolling the fuel-air ratio of the mixture supplied to the engine.

Automatic choke devices operable to move a choke or air inlet valve todifferent positions in response to variations in engine temperatureand/or suction are commonly provided in carburetors at the present time.These devices generally include an unbalanced valve in the carburetorair inlet which is subject to pressures created by the air entering thecarburetor, is also controlled by a thermostat which exerts a force tohold the valve closed at low temperatures and also by a suction operatedmember connected to the valve and responsive to variations in suctionposterior to the throttle, which exerts a force tending to open thevalve as such suction increases.

it is the purpose of the present invention to provide a carburetorhaving a choke valve and means for automatically positioning the chokevalve in response to variations in temperature and engine suction whichincludes a suction operated member which is effective to move the chokevalve to a predetermined position, when the engine is started with thechoke valve in closed position, but which is rendered substantiallyinefiective at such predetermined position of the valve, so that for aconsiderable part of the opening movement of the choke valve, thesuction operated means is ineffective and again becomes effective afterthe choke valve has made a further predetermined opening movement.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

Figure 1 is a vertical section, partly in elevation, of a conventionaldown-draft carburetor, embodying the present invention; and

Figure 2 is a detail section on the line 2-2 of Figure 1.

This application relates to a device which might be considered animprovement on the device disclosed in the application of Lawrence C.Dermond, S. N. 438,771, filed lune 23, 1954, new Patent No. 2,808,244,dated October 1, 1957. In the device disclosed in the Dermondapplication, a piston which is connected to the choke valve is slidablein a cylinder to which the engine suction, which is maintained posteriorto the throttle, is communicated through a conduit which connects withthe side of the cylinder at such a point that the conduit is blocked bythe piston after the relatively small movement of the choke valve, whichtakes place when the engine first becomes self-operative. This rendersthe suction conduit substantially ineffective and it remains ineffectivethroughout the remainder of the opening movestem:

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ment of the choke valve which is effected by the pressure differentialacross the choke valve itself as the engine temperature progressivelyincreases and the force of the thermostat is reduced.

In some installations, this mechanism does not effect opening of thechoke valve rapidly enough after the valve reaches a certain positionand the mixture becomes slightly too rich for best engine operationduring the latter part of the engine warm-up period and the last 20 to30 degrees of movement of the choke valve. In the device disclosed andclaimed in this application the means for communicating suction to thepiston, such as disclosed by Dermond, is rendered ineifective in justthe same way as in the device of Dermond, but is rendered effectiveagain after the choke valve is approximately 60 degrees open and remainsefiective throughout the rest of the movement of the valve to its fullopen position. This results in somewhat more rapid movement of the chokevalve toward open position in that part of its operating range, above 60degrees'open, and produces a slightly leaner mixture in that part of thevalves movement.

Except for the change in the operating means for the choke valve whichhas been referred to, the device disclosed is of just the sameconstruction as that shown in the Dermond application, but it should benoted that as shown, the position of the fuel supply tube which conveysfuel from the fuel chamber to the fuel inlets has been reversed and suchtube is at the right side of the fuel chamber, as seen in Fig. 1 insteadofon the left side, as in Dermond.

The carburetor comprises three castings, 2, 4 and 6 suitably securedtogether by screws 8, or in any suitable way. The casting 2 is the airinlet casting having a passage 1.0 for admission of air. The casting 4is the fuel chamber casting and has a constant level fuel chamber 12therein, in which fuel is maintained at a substantially constant levelby mechanism which will be very briefly described later. The passage 10communicates with a chamber or passage 14 centrally located in thecasting 4 into which fuel is introduced and which forms the mixingchamber of the carburetor.

The casting 4 is immediately above and secured to the casting 6, whichis the outlet casting, and is secured in any suitable way to the intakemanifold of the engine. An outlet passage 16 is formed in the casting 6and connects with the passage 14, the passages 10, 1.4 and 16, forming acontinuous intake passage through the carburetor through which airentering the inlet flows and is mixed with fuel to form a combustiblemixture which flows through the outlet passage 16 to the engine:

The flow of mixture from the carburetor is controlled by a suitablethrottle valve 18 secured to a shaft 20 suitably journalled for rotationin the Walls of casting 6. This throttle is manually operated in theusual manner by means of an arm 22 secured to one end of the shaft 20and is variably positioned to control the volume of mixture supplied tothe engine and the speed thereof.

Fuel is supplied to the fuel chamber 12.through a passage 24 formed inthe wall of casting Z and communicating with this passage is a nipple 26threaded in the wall of casting 2 and having a passage 28 which conveysfuel from passage 24 to chamber 12. The nipple 26 is enlarged at itslower end to form a cylindrical chamber 30 in which is received a valve32 which controls flow through passage 28. This valve is freely movableand its lower end rests on a tang 34 cut out from an integral with aplate or bracket 36 which is secured to a float (not shown), and ispivoted on a pin 38 mounted in lugs 40 which are integral with anddepend from the casting 2 into the chamber 12. When the fuel reaches apredetermined level, the float' is raised enough to move the valve 32against its seat to close passage 28. This is a conventional float valveconstruc tion and forms no part of the present invention.

A tube 42 is secured at its upper end in any suitable way to an annularrib 44 projecting from the casting 2 and has a fuel passage 46 formedtherein to conveyifuel from the chamber 12 to the carburetonmixingchamher. A calibrated plug 48 is screwed lintothe lower. end of tube 42and meters the fuel supplied to thernixing chamber. The passage as, atits upper .end, connects with a cross-passage 50 formed in a bridge.member-52 which extends across the mixing chamber and is integral withthe casting 2. The passage 50 supplies fuel tothe main nozzle 54 whichextends into a small venturi tube 56 positioned in the mixing chamberand extending into alarge venturi 57 which forms the wall of the mixingchamber. A plug 58 having a restricted orifice therein ispositioned inthe main nozzle to aid in atomizing the fuel. Air is admitted to thepassage 50 through two small passages 60 to mix with the fuel flowingtherethrough. i

Positioned in the-bridge piece 52 at the right of the main nozzle is asleeve 62 having a passage therethrough for idling fuel and at its rightend, this sleeve is somewhat reduced insize so that it is spaced fromthe wall of the passage 50, as shown in Fig. l. The fuel which flowsthrough the sleeve 62 ultimately reaches the passage 64 which suppliesfuel to idling fuel supply inlets (not shown),.which deliver fueladjacent the edge of the throttle valve 18.

The admission of air to-the passage is controlled by an automaticallyoperated choke valve 70 secured to a shaft .72 suitably journalled forrotation in the wall of the casting 2. This shaft has secured to theleft end thereof, as seen in Fig. 1, an arm 74 which has a horizontallyextending portion 7 6. The shaft 72 extends into a housing-78 which is apart of casting 2 and is provided-with a removable and adjustablecover-plate 80 which may be.either metal or a suitable plastic and isheld in any adjusted position by screws 82. The arm 76 at the end of thechoke shaft and cooperating parts, about to be, described, arepositioned in this housing.

The arm 76 is engageable by the hooked end 84 of a thermostat 86, theother end of which is secured to a pin 88 .which is fixed. inthecover-plate 80, as shown in Fig. 1. Upon reduction of temperature, thehooked end 84 moves counter-clockwise to engage the extension 76 of arm74 and exerts a pressure thereon to hold the choke valve in closed.position, as shown in Fig. 2. By adjustment of wplatetsll, the pin 83 isrotated and changes the pressure exerted by the thermostat at any giventemperature to hold the choke valve closed.

The lower end of the arm 74, as seen in Fig. 2, i pivotally connected toa link 96 which is pivotally connected to a cross-pin 92 extendingacross a slot 93 in the right end of a piston 94 slidable in ahorizontal cylinder 96 integral with the housing :78 and to which thesuction maintained inthe intake passage posterior to the throttle 18 iscommunicated through a passage 98. The passage. 98 may connect with thecarburetor outlet between the throttle and the manifold or with theintake passage in the manifold itself. The particular positionof thisconnection is not material as long as it is on the engine side of thethrottle.

The mechanism so far described is substantially the same as that shownin the Dermond application previously referred to.

In the device disclosed herein, the passage 98 connects with thecylinder 96 by means of an orifice 100 in the side Wall of the cylinder.This orifice is of rectangular shape, as shown, but may be triangular orof any other shape desired, and the orifice is positioned relativelyclose to the position occupied by the end of the piston when the chokevalve is in its closed position, so that the orifice will be blocked bythe side wall of the piston when the choke valve has made a. relativelysmall opening movement, approximately 20%, for example. When the passageis'blockedasdescribed, there may be some slight leakage past the pistonso that some degree of suction might be communicated to the space 1432at the left of the piston, but there would also be leakage of air pastthe piston from the right end thereof so that any eifect of suction inthe space 102 is substantially nullified. Therefore, after the pistonreaches the position where the orifice 10b is blocked, there issubstantially no force produced by suction which is then effective tomove the piston further to the left.

The choke valve will be moved to a position to block the orifice 100substantially immediately after the engine starts to run under its ownpower and this position of the valve is that which has been found mostdesirable for the valve to occupy at the beginning of the warmupoperation of some particular engine. For some other engine, it might bedesirable for this movement of the choke valvelto be increased ordecreased and this can be accomplished within limits, by changing theposition of the orifice 100.

There maybe some slight difference in the position assumed by the chokevalve, when it is first moved by engine suction immediately after theengine becomes selfoperative, due to the difference inthe force exertedby the thermostat at different temperatures. This will be very slight,however, andthe high suction effective immediately after the enginestarts to run is always effective to move the valve to a position asmuch as 20% open so that the opening will be blocked by the piston atpractically any temperature which may be encountered when starting.

If the suction which is communicated to the cylinder through orifice 100continued to be effective on the piston after thechoke valve has beenopened to the extent referred-to during the engine warm-up period, ithas been found that in some installations the opening of the valve,in-this part of its operating range, would be too rapid and the mixturesupplied to the engine would be too lean. To prevent this occurrence,the Dermond device was designed and the construction is much the same inthis device. After the orifice 100 is blocked when the valve is about20% open, the subsequent rate of movement of the valve is controlledprimarily by the rate at which the thermostat is heated. After thepassage 100 is blocked by the piston, further movement of the valvetoward open position is brought about solely by the effect of thepressure differential across the valve and this movement will take placeonly as fast as the force of the thermostat opposing such movement isprogressively reduced, as the thermostat is heated.

To heat the-thermostat, heated air is drawn through the housing 78 andto this end the suction passage 98 is connected with the interior ofhousing 78 by a passage 104 formed in the Wall of the housing, asindicated in Fig. 2. The suction which is maintained in the passage 98is communicated to the space in the housing 78 and is effective to drawheated air from a conventional exhaust pipe stove (not shown) through aconduit 106 and through passage108 formed in a threaded nipple 110projecting from housing 78 to which conduit 106 is connected by anysuitable coupling means. As this heated air is drawn through the housing78, the force exerted by the thermostat to hold the choke closed becomesprogressively less and the valve moves toward open position at a speeddependent solely upon this reduction in the force of the thermostat,unless the throttle is moved toward open position. If the throttle is somoved, there will be an increase inthe pressure differential effectiveon the choke valve which-would cause it to move more rapidly toward openposition. At the same time, there would be a reduction in the suction inpassage 93 and a slower flow of hot air through housing 78, with-slowerheating of the thermostat, but this would be more than offset bytheincrease in opening pressure directly onthe valve.

During its movement from a position about 20 open to a position about 60open, the passage 100 is blocked by the wall of the piston, but when thevalve reaches the latter position a passage 112, extending through thepiston wall to a central bore 114 therein, which extends for aconsiderable portion of the pistons length, is brought into registrywith the passage 100. As soon as this takes place, whatever suction ismaintained in the passage 98 is communicated to the space 102 with theresult that after the choke valve reaches a position about 60 open, itsmovement toward further open position is stepped up by the eflect ofsuction, so as to prevent any tendency to form an over-rich mixtureduring the latter part of the engine warm-up period when the choke valveis approaching wide-open position.

The point in the range of movement of the choke valve at which thepassage 112 becomes effective can be changed by changing the position ofsuch passage with reference to the length of the piston and the extentof movement of the valve after the passage 112 becomes effective can bemodified by changing the shape or area of the passage. In other words,the passage 112 can be of such shape and/or size that it remains inregistry with the passage 100 until the choke valve is fully open or itcan be designed to go out of registry with passage 100 before the chokevalve reaches wide-open position, if it be so desired.

In the device, as shown, when the choke approaches closely to full-openposition, a groove or cut-away part of the piston 116 moves intoregistry with the passage 100, so that when the coke is in such positionheated air is drawn more rapidly through housing 78 than during theopening movement of the choke, but this passage has no controllingeffect on the rate of movement of the choke valve toward open positionas a similar passage has in the earlier Dermond device. In this device,the valve is substantially fully open before the groove 116 becomeseifective, while in the Dermond device such groove becomes eflectivewhen the choke valve is about open.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

In a charge forming device for internal combustion engines having aconstant level fuel supply chamber, an intake passage having fuel andair inlets and a mixture outlet for supplying a combustible mixture tosaid engine, a throttle valve for controlling the flow of mixture to theengine and a choke valve for controlling the admission of air throughsaid inlet; mechanism for automatically controlling the operation ofsaid choke valve comprising thermally responsive means operable to holdthe valve closed at low temperatures, a suction operated piston slidablein a cylinder and connected to the choke valve so as to effect movementthereof when the piston is moved in one direction, a suction passage inthe wall of said cylinder, said suction passage being so positioned thatit will communicate the engine suction to one end of the piston when thechoke valve is in closed position, said piston including a land adaptedto completely block said suction passage to prevent suction from movingsaid piston after the choke valve has made a predetermined openingmovement, and a passage in the wall of the piston movable into registrywith said suction passage after the choke valve has made a furtherpredetermined opening movemerit, said passage being effective to againcommunicate the engine suctionto the piston to effect opening of thechoke valve.

References Cited in the file of this patent UNITED STATES PATENTS

